(a) Field of the Invention
The present invention relates to liquid crystal compounds including vinylcyclohexylbenzene and its derivative, and the preparation method for the same. More particularly, the present invention relates to liquid crystal compound used for liquid crystal display (LCD) having fast response time, wide phase-transition temperature and low viscosity by controlling physical property at a high clearing temperature.
(b) Description of the Related Art
The liquid crystal compound is essential material for liquid crystal flat display and is an organic compound with electro-optical characteristic that has a fluidity in liquid and anisotropy in crystal. When applying voltage to upper and lower electrodes, the change in alignment of liquid crystal compound also changes the transmission of light emitted from the backlight, thereby forming an image.
The liquid crystal composition is a mixture of about 20 liquid crystal compounds having a molecular weight of 200 to 600. The LCD using the liquid crystal composition as an essential material are displays with 20 to 30-inch panel such as laptop, monitor, mobile phone and etc., and TV or large-sized advertising display with large-sized panel, for examples 30 inches to 100 inches. The liquid crystal composition can be applied for various displays and is highly marketable product. In addition, the market of LCD expands from the polar region to the vicinity of equatorial region.
To keep the marketability of LCD product, the liquid crystal compounds must meet the requirements such as fast response time and wide operating temperature range which are suitable for TV to show fast-moving image rather than monitor or laptop.
Liquid crystal medium must have fluidity of mesophase as liquid and anisotropy as crystal (refractive index and dielectric constant). The liquid crystal compound preferably includes a central backbone such as cyclohexyl, phenyl, naphthalene, pyridazine or dioxaborane, and etc, and a side chain such as alkyl, alkoxy, alkenyl, halide, CN, NCS, and etc. The liquid crystal medium has various mesophase and temperature ranges depending on the combination of components.
As the number of cyclohexyl group or phenyl group included in the liquid crystal compound increases, the clearing temperature at mesophase or solid phase increases.
U.S. Pat. No. 4,556,745 discloses that introduction of ethylene group (—CH2CH2—) to central backbone can lower the viscosity. In addition, the conventional patents introducing ethylene group (—CH2CH2—) to central backbone are U.S. Pat. Nos. 4,035,056, 4,261,651, 4,439,015 and 4,482,492. As disclosed in the patents, a compound including “—C(O)CH2—” group in a central backbone is prepared by acylation method, and then ethylene group is introduced by the reduction method.
U.S. Pat. Nos. 4,431,853, 4,583,826, and 4,460,770 disclose that the ethylene group (—CH2CH2—) is introduced to central backbone by bromination and Grignard reaction after reducing carboxylic acid compound.
In U.S. Pat. Nos. 4,439,015, 4,550,981, 4,460,770, 4,583,826 and 4,652,089, liquid crystal compound including ethylene group (—CH2CH2—) at central backbone is prepared by introducing ethenyl group (—CH═CH—) to central backbone with using triphenylphosphine (hereinafter, PPh3) and aldehyde compound, and then by performing catalytic reduction. In case of using triphenylphosphine in the preparation of liquid crystal compound, most products include cis-ethenyl group. The cis-compound must be converted to trans-isomer to be used for a liquid crystal medium.
Accordingly, in JP Patent No. 3,002,429, the epoxide compound is prepared from cis-ethenyl group by using peroxides as an oxidant, and most of the compounds in trans-form are obtained by converting them with PPh3.
However, because the produced trans-isomer includes a small amount of cis-isomer, several purification steps such as recrystallization must be performed to obtain pure trans-isomer.
In addition, U.S. Pat. No. 6,348,244 discloses that the compound with ethylene group in central backbone is prepared by reacting aldehyde compound with Grignard reagent and catalytic reaction, or by using n-butyllithium compound. U.S. Pat. No. 4,621,901 discloses that alkenyl group is introduced to the end of liquid crystal compound. However, the preparation methods disclosed in the documents have complex problems in preparation procedure and recrystallization.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.